The invention concerns a centrifuge with a self-evacuating drum, with a line for feeding the drum with the stock to be centrifuged, with at least one outlet line with an elastic section for extracting a liquid phase from the drum under pressure, and with a mechanism for expelling solids from the drum at prescribed intervals.
Such centrifuges are generally known. The solids can be expelled in what are called fractional evacuations, whereby only a small fraction of the drum's contents is removed. This procedure suddenly reduces the pressure in the drum and accordingly in the outlet line, which can be detrimental to downstream equipment.
In skimming milk as described in German C 3 539 485 for example, the skimmed milk is forwarded to a heater, and heat is also transferred to the starting milk. Regulations require that the pressure at the pasteurized skim-milk end must always be higher than the pressure at the starting-milk end. This condition cannot for the aforesaid reasons be satisfied during the evacuation procedure.
A centrifuge is known from FR A 1 481 803 with a volume limiter that stretches to a certain extent in the feed line and another in at least one outlet line. The volume limiter is intended to prevent variations in the ratio between the volumes in two outlet lines when the pressure changes. These mechanisms cannot, however, compensate for a sudden reduction in pressure in an outlet line as occurs in conjunction with centrifuge drums with solids-expulsion mechanisms during the expulsion procedure. The elastic deformation of the outlet line and the associated variation in volume are so slight in relation to the materials generally employed that no effect on the pressure reduction is to be expected.
German A 2 151 475 describes a valve with a tubular diaphragm that can be subjected to external compressed air in order to vary the valve's channel and hence the rate of the fluid flowing through it. Valves of this type are also appropriate for maintaining a constant pressure in a line with a fluid flowing continuously through it. When the flow is interrupted as occurs while solids are being expelled from the drum and into the outlet lines in a centrifuge, however, such a reduction in pressure cannot be prevented.